Trait-based prioritization of native herbaceous species for restoring biodiversity in Mediterranean olive orchards

A major land use in Southern Spain is olive cultivation with intensive practices and simplified agroecosystems with limited sustainability. In the same region, there is a rich native flora which offers many species that are compatible to use as cover crops in the olive orchards. Native forb cover crops have the potential to restore biodiveristy and improve long-term sustainability by decreasing external inputs and improving the health of the soil and supporting populations of beneficial insects. However, native Mediterranean forb species remain understudied and underutilized. In this work, the objectives were to characterize native forbs for traits of interest: germination behavior, seed biology, plant establishment and agronomic traits and apply those results to use and test a species selection tool. The seeds of winter annuals are generally dormant upon dispersal, lose dormancy in summer through after-ripening, and germinate in early winter. Under semi-dry Mediterranean climate with dry-hot summers and cool-wet winters, many forbs with potential for habitat restoration are winter annuals, but there is very little information about their germination. We calculated hydrothermal thresholds from germination responses to temperature, after-ripening and water stress of 13 ruderal dicots native to Andalusia (southern Spain), measuring the germination of fresh seeds from natural populations across nine temperature treatments, from 5C to 35 °C, constant and alternate, and the effect of after-ripening and water stress. Final germination ranged from 0-100% and results were mixed in response to temperature. Base temperature was below 6 ºC, optimal temperature was around 14 ºC and the ceiling temperature around 23 ºC. For five species, 10 months of after-ripening improved total germination, indicating a dormancy-breaking effect, but the other species did not respond or had their germination reduced. All species were tolerant to water stress, with base water potential ranging from -0.8 MPa to -1.8 MPa. Our results suggest that hydrothermal germination thresholds, rather than physiological dormancy, are the main drivers of germination phenology in annual forbs from Mediterranean semi-dry environments. Given known temperature and water conditions, it is possible to predict the germination of these forb species. The higher variability of germination response compared to annual grasses is a possible consequence of the natural and anthropogenic disturbances in ruderal habitats. (Chapter 1). Seed farming, the large-scale mechanized cultivation and harvest of wild species for seed production, is necessary to generate native seed mixes that are appropriate, affordable and consistently available for use in ecological restoration. Due to the diversity of wild species and their non-domesticated status, trial evaluations can help determine which species and which cultural practices are most suitable for seed farming. In Mediterranean habitats, forbs have the potential to enhance biodiversity and provide ecosystem services yet remain understudied and underutilized for ecological restoration. We evaluated 27 Mediterranean dicots for four main characteristics important to seed farming: establishment, growth form, phenology and yield. Row spacing was adequate for 19 species but could be improved for eight. Twenty-four species have fruit height suitable for mechanized harvest while fruits are too low in three species. The time from sowing to seed maturity varied among species and harvest windows were one to six weeks long. Seed yield ranged from 2 g/m2 to 55 g/m2. The results provide seed producers with useful recommendations for sowing rate, row spacing and harvest time for each species. Characterization of seed farming traits for these native forbs provides a starting point to stimulate the native seed production sector. Seed supplies of native species are needed for applications such as restoring biodiversity, ecological restoration...